A communication system is arranged for provision of communication connections between two or more entities such as user terminal equipment and/or other nodes associated with the system. The communication may comprise, for example, communication of voice, electronic mail (email) and text messages, multimedia and so on. A communication system may provide communication over a fixed line or wireless interface for user terminals or other nodes. An example of systems carrying wireless communication is the public land mobile network (PLMN). An example of the fixed line networks is the public switched telephone network (PSTN).
A communication system typically operates in accordance with a given standard or specification which sets out what the various elements of the system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely, user equipment or terminal is provided with a circuit switched (CS) service or a packet switched (PS) service or both. Communication protocols and/or parameters which shall be used for the connection are also typically defined. For example, the manner how communication shall be implemented between the user equipment and the elements of the communication network is typically based on a predefined communication protocol. In other words, a specific set of “rules” on which the communication can be based on needs to be defined to enable communication by means of the communication system.
Examples of the different standards and/or specifications for wireless communication include, without limiting to these, specifications such as GSM (Global System for Mobile communications), AMPS (American Mobile Phone System), DAMPS (Digital AMPS), various GSM based systems such as the GPRS (General Packet Radio Service). The so called 3rd generation (3G) standards include systems such as the WCDMA (Wideband Code Division Multiple Access) based UMTS (Multiple Access in Universal Mobile Telecommunications System), IMT 2000 (International Mobile Telecommunications system 2000), i-Phone and so on.
In a typical wireless cellular communication system a base station of a radio access network serves user equipment such as mobile stations or similar terminal apparatus via a wireless interface. Each of the cells of the cellular system can be served by an appropriate transceiver apparatus, typically, but not always, referred to as a base station (BS). The base station may be connected to and controlled by a controller entity. For example, in the GSM radio network a base station is connected to and controlled by a node referred to as a base station controller (BSC). The BSC node may in turn be connected to and controlled by a mobile switching center (MSC), a serving GPRS support node (SGSN) or similar facility. It shall be appreciated that the controller entities may be provided by means of appropriate server entities. For example, functions of a MSC may be provided by a MSC server (MSS).
The communication link between a user equipment and the network, i.e. the so called user-to-network leg is typically controlled by at least one controller entity. The leg may be controlled e.g. by means of a home or a visited MSC or a MSS media gateway (MGW). When setting up a communication path between two user equipment via the communication network the communication mode of the legs at both ends of the path are set up and synchronised so that a desired mode of communication can be provided for the users. For example, the calling user may wish to have a speech connection or a video or other multimedia connection with the called user, and the connection is then set up accordingly.
The prior art also suggest a fallback behaviour by means of which a call can be returned to speech mode in case an attempt to establish a multimedia call fails. By means of this feature a calling user does not need to know whether the called party supports or wants to receive a video or other multimedia call, because in this case the call would automatically fall back to a speech call. If the fallback feature is not provided, the call set-up would then simply fail.
The users may also wish to be able to change e.g. from the speech mode to the multimedia mode during an ongoing call. This is enabled e.g. by means of the so called SWAP scheme wherein users can start the call either with speech or with multimedia, and then swap from speech to multimedia and vice versa during the call. More particularly, e.g. in the SWAP scheme the users can swap from speech to multimedia and vice versa by initiating the change at both end legs of the connection. The swap between modes needs to be accomplished locally at each of the end legs between the respective mobile stations and the visited mobile switching centre entities. This is so since in the proposed solution the fixed network leg between the wireless legs may offer a substantially constant 64 kbit/s transmission throughout a call, that is the mode of the fixed leg is not changed even if the mode of the legs needs to be changed.
The inventors have found that the change of the modes may not operate satisfactorily in the prior art communication systems, and that the users might wish to obtain an improved solution for the change of modes. For example, if the call is done within a 3GPP (third generation partnership project) Release 4 split core network architecture i.e. in a system involving elements such as a MSC Servers (MSS) and Media Gateway (MGW) network elements, the swap procedure requires an in-call bearer modification procedure. This procedure is required to be used in order to be able to dynamically modify characteristics of a user plane (i.e. the Nb interface) connection (codec) between the MGWs associated with the connection.
The inventors have found that a multimedia call cannot be started whit a speech-only mode provided with the current ISUP (ISDN User part) signalling and BICC (Bearer Independent Call Control), and that the current ISUP and BICC do not support switching (“swapping”) between speech and multimedia modes. Consequently, the synchronisation of the possible swaps at both end legs of the connection is left to the users. The users, for example, need to agree verbally on the swap. Both users need then activate manually an appropriate radio channel modification procedure at their terminals or even setup a new call in the desired mode.